An equipment for expanded cracker manufacture is notably described in Belgian Patent BE-A-1000311 and in European Patent EP-A-0359740, which are both assigned to the same inventor as the present invention.
The basic components of the equipment disclosed in said documents is incorporated herein by reference and do form the starting point of the present invention.
The previously proposed machine improvements in BE-A-1000311 mainly concerned the provision of a novel hydraulic drive and control unit formed of two aligned double-action cylinders, integrally assembled in one drive block and capable of selectively displacing the common drive shaft thereof in controlled sequential steps. Said drive shaft actuates a toggle-mechanism that is connected to a lower punch for slidingly reciprocating the same in and out of a mould cavity defined in a fixed upper mould. An adjustable micro-switch contact may be provided between the upper toggle arm and a switch support on the machine frame to control the end of the driving stroke of one of the operating cylinder pistons and hence the uppermost compression position of the punch. Said drive and control arrangement ensures a reliable continuous operation of the machine without risk of overload and enables the obtainment of uniformly expanded crackers of constant thickness.
In EP-A-0359740 there is further disclosed a unique three-part mould configuration, characterized by a separately actuated peripheral mould element constituting thus a movable peripheral side-wall of a fixed upper mould. Said peripheral ring mould is capable of being tightly pressed against a heatable fixed upper mould plate and of slidably receiving a lower heatable punch for crushing and pressure-baking a given quantity of granular material in the hermetically closed, heated chamber formed by the three cooperating mould elements. At the expansion stage of a cracker production cycle the punch is quickly drawn back a small distance within said chamber which is still closed, and thereafter the ring mould is slided downwards along the partially withdrawn punch received therein, which are then both lowered until the expanded cracker resting on the punch head can be readily discharged therefrom by a pushing element of the grain feeding slide. Said arrangement has the important advantage of efficaciously solving the unpredictable occurence of mould sticking, which was hereto a major cause of inferior cracker quality, mould contamination and frequent machine downtime. Notwithstanding the already achieved significant improvements, there was still a large need for further developments in such equipment. For mass production of different cracker types a better control of baking pressure and expansion conditions was required, especially at increased production rates, and in this connection a flexible and efficient control was needed to cope with unavoidable variations in grain feed and cereal type parameters. Furthermore there was a real need for increasing the production capacity of a single machine unit, bearing in mind that its advanced hydraulic drive .and control means is an expensive piece of technology.
Indeed, when operating an equipment as discribed in EP-A-0359740 at higher speeds, machine perturbations and poor cracker quality was often noticed, which was assumed to be due to a too slow reaction velocity of the hydraulic drive system and to undesirable variations of final baking pressure due to the previously used microswitch system for controlling the end point of the forward stroke of the actuated drive piston. The latter was assumed to be due to inevitable mechanical straining (elasto-plastic) of repeatedly stressed machine parts, incl. the toggle-mechanism, and further to certain variations in cereal supply conditions (grain size, volume, weight; cereal type) which affect the grain crushing "strength--strain" curve and hence the attainable pressure in the mould for a preset adjustment position of the microswitch end control means. To overcome these remaining deficiencies the present inventor came to the finding, after extensive studies and trials, that an improved design of the hydraulic system of the drive unit was necessary, including the provision of a novel means for controlling the end point of the pressurizing stage. Furthermore the need of a greatly increased cracker-production capacity of a single machine or of a production line comprising plural machines, could be met in a most effective way by a novel twin-head mould-configuration of the present invention, which solution was found to be far superior and most reliable in comparison with numerous other (theorktical and practical) possibilities for raising machine output such as higher drive speeds, shorter baking cycles, multichamber dies (cf. FR-A-2017014) and the like; these alternatives proved to be unsuitable for continuous high-rate cracker production because of mechanical and hydraulic deficiencies, incl. inconsistent production quality.